Objective for video disks

ABSTRACT

An objective for video disks comprising five lens components of single lenses for which the numerical aperture on the recording surface side is large, working distance is large and aberrations especially spherical aberration and coma are corrected favourably. Besides, said objective for video disks is arranged so that it can be used also for rays from infinite distance by varying an airspace between a second and third lens components.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an objective for video disks and, moreparticularly, to an objective for video disks with high reduction ratioto be used for recording the modulated signals when making a master diskof photoelectric video disks.

2. Description of the Prior Art

For recording of modulated signals for making the master disk ofphotoelectric video disks, an objective designed exclusively for saidpurpose has not yet been known and, therefore, microscope objectiveshave been generally utilized for the purpose. Due to the fact that asingle wavelength in the range of 435.8 nm (g line) to 486.1 nm is usedas the recording signal wavelength for recording of modulated signals,it was possible to obtain recording results of somewhat satisfactorylevel even when such microscope objectives are used. However, microscopeobjectives have many cemented lens surfaces therein and, moreover, theirchromatic aberration is corrected in respect to rays in the range ofvisible radiation. Therefore, by microscope objectives, it is impossibleto record the signals with high accuracy because of the influence ofaberrations. Especially when a ray in ultraviolet range (for example, aray of wavelength 351 nm) is used for the purpose of high-densityrecording, absorption of light by the binding agent used on saidcemented surfaces occurs in addition to influence of chromaticaberration and, consequently, transparency decreases.

Regarding the performance of objectives for recording, the followingproperties are especially required: (1) transparency should be high forrays up to the near ultraviolet radiation or up to the ultravioletradiation, (2) the resolving power should be high, (3) influence ofdiffracted rays other than the zero order should be minimized, and (4)contrast of the image should not decrease.

To satisfy the requirement (1) out of the above, it is necessary toselect a proper glass material and to prevent absorption of light by thebinding agent on the cemented surface. As for the requirement (2), it isnecessary to make the numerical aperture as large as possible. As forrequirements (3) and (4), it is necessary to correct aberrationsfavourably and to minimize spherical aberration and coma especially. Asfor the requirement (4), it is further required to prevent flare. Whenthe objective has a cemented surface, condition of cementing should betaken into consideration in addition to transparency, flare, etc.Because, if the cemented condition of the cemented surface is not good,noise corresponding to the cemented condition will be recorded togetherwith the modulated waves. Moreover, as the incident light is convergedinto a fine beam, energy of light which passes through a unit area ofrespective lens surfaces is extremely large and, consequently,disconnection of cemented surface may be sometimes caused.

A master disk for recording is made of a base disk of metal, glass, etc.coated with a light-sensitive agent such as "Photoresist". The surfaceof said light-sensitive agent is exposed to the modulated light whichhas passed through and been converged by the objective. In case ofmodulated laser beam, the beam which reaches the surface oflight-sensitive surface is converged to a diameter of 1 μ or less.Therefore, temperature of the portion exposed to the beam becomes veryhigh and the light-sensitive agent will be evaporated. If the evaporatedmatter sticks to the objective, contrast of image and resolving power ofthe objective will decrease.

SUMMARY OF THE INVENTION

It is, therefore, a primary object of the present invention to providean objective for video disks comprising single lenses only and,therefore, not having a cemented lens surface for which the numericalaperture on the recording surface side is large and, moreover, for whichthe working distance is comparatively large.

The objective for video disks according to the present invention is alens system of five-component five-element lens configuration comprisingsingle lenses which are divided into a front lens group and rear lensgroup by providing a large airspace between said front and rear lensgroups. Said front lens group comprises a first, second and third lenscomponents, said first lens component being a biconvex lens, said secondlens component being a negative lens having a concave surface of strongnegative refractive power which is concave toward said first lenscomponent, said third lens component being a biconvex lens. Said rearlens group, comprises a fourth lens component and fifth lens component,said fourth lens component being a positive meniscus lens which isconvex toward said front lens group, said fifth lens component being apositive meniscus lens which is approximately hemispherical and isconvex toward said fourth lens component. Besides, the objective forvideo disks according to the present invention is arranged to satisfythe following conditions when reference symbol f represents the focallength of the lens system as a whole, reference symbol f_(F) representsthe total focal length of the front lens group, reference symbol f_(R)represents the total focal length of the rear lens group, referencesymbol r₂ represents the radius of curvature of the rear surface of thefirst lens component, reference symbol r₃ represents the radius ofcurvature of the front surface of the second lens component, referencesymbol d₂ represents the airspace between the first and second lenscomponents, and reference symbol d₆ represents the airspace between thefront and rear lens groups.

    1.19 ≧ d.sub.6 /f ≧ 0.62                     (1)

    3.7 ≧ f.sub.F /f ≧ 2.7                       (2)

    0.29 ≧ f.sub.R /f.sub.F ≧ 0.19               (3)

    0.86 ≧ |r.sub.3 |/|r.sub.2 | ≧ 0.6                                              (4)

    0.15 ≧ d.sub.2 /f ≧ 0.11                     (5)

In the lens system as described in the above, the front lens group isarranged to chiefly correct chromatic aberration, and it is possible tocorrect chromatic aberration by making the refractive index of the lenshaving negative refractive power different from refractive indices oflenses having positive refractive powers or by making the refractiveindex of the lens having negative refractive power large. For example,it is desirable to make the difference n₂ - n₁ between the refractiveindex n₁ of the first lens component and refractive index n₂ of thesecond lens component as n₂ - n₁ ≧ 0.15 and the difference n₂ - n₃between the refractive index n₂ of the second lens component andrefractive index n₃ of the third lens component as n₂ - n₃ ≧ 1.5 and tomake Abbe's numbers ν₁, ν₂, and ν₃ of the first, second and third lenscomponents respectively as ν₁ > 55, ν₂ > 40 and ν₃ > 55. When, however,the refractive index n₂ of the lens having negative refractive power ismade too large, transparency will decrease in case of some kinds ofglass materials. Therefore, especially for dense flint type glassmaterials, it is necessary to make said refractive index n₂ as n₂ < 1.7.

The rear lens group is to converge the rays from the front lens groupand, therefore, the energy per unit area of rays which pass through eachlens component will become high. So, it is necessary to preventdeterioration of the lens system by using, for example, fused quartz aslens material.

Besides, in the present invention, it is possible to favourably correctaberrations of the lens system as a whole balancing said aberrationsfavourably by arranging so that the lens system satisfies theafore-mentioned respective conditions.

If the airspace d₆ between the front and rear lens groups in thecondition (1) becomes d₆ /f > 1.19, astigmatism will be correctedfavourably. However, it is not desirable because spherical aberrationand coma will tend to be overcorrected. If, on the contrary, it becomesd₆ /f < 0.62, astigmatism will be aggravated and will become a verylarge positive value progressively toward the marginal portion.Moreover, the astigmatic difference will increase.

If, in the condition (2), the total focal length f_(F) of the front lensgroup becomes f_(F) /f > 3.7, coma will tend to be overcorrected. If, onthe contrary, the total focal length f_(F) becomes f_(F) /f < 2.7, comawill tend to be undercorrected.

If, in the condition (3), the ratio f_(R) /f_(F) of the total focallength f_(R) of the rear lens group to the total focal length f_(F) ofthe front lens group defined by the above-mentioned condition (2)becomes f_(R) /f_(F) > 0.29 exceeding the upper limit, paraxialspherical aberration at the marginal portion will be undercorrected. If,on the contrary, the ratio f_(R) /f_(F) becomes f_(R) /f_(F) < 0.19,asymmetry of coma will be caused.

The condition (4) relates to the ratio |r₃ |/|r₂ | between the radius ofcurvature r₂ of the rear surface of the first lens component and theradius of curvature r₃ of the front surface of the second lens componentand is established for the purpose of correcting chromatic aberrations.If it becomes |r₃ |/|r₂ | > 0.86 in the condition (4), chromaticaberration will tend to be undercorrected. If it becomes |r₃ |/|r₂ | <0.6, chromatic aberration will tend to be overcorrected. For correctionof chromatic aberration, of course it is desirable to make thedifference between refractive indices of the first and second lenscomponents large, i.e., n₂ - n₁ ≧ 0.15 as described before. Moreover, itis easier to correct chromatic aberration of spherical aberration whenthe radius of curvature r₂ of the rear surface of the first lenscomponent is selected within the range of 1.6 ≧ |r₂ |/f ≧ 1.3.

As for the condition (5), spherical aberration will be undercorrectedand the astigmatic difference will increase if the airspace d₂ betweenthe first and second lens components becomes d₂ /f > 0.15. If theairspace d₂ becomes d₂ /f < 0.11, astigmatism will be aggravated andwill become a very large value progressively toward the marginalportion.

The above-mentioned objective for video disks according to the presentinvention is arranged to focus an image of a light source located at alimited distance onto a recording surface. To make a master disk forphotoelectric video disks, it is sometimes required to record the raysfrom infinite distance. If the above-mentioned objective for video disksis used for rays from infinite distance as it is, aberrations will beaggravated. To arrange the objective, which is designed for recordingthe rays from the light source at a limited distance, so that it can beused also for rays from infinite distance also in favourable state, thefollowing methods may be considered.

One method is to additionally provide a negative lens, which has thefocal point at the position of the light source located at a limiteddistance, on the object side of the objective. By this method, paraxialrays from infinite distance passed through the added negative lensbecome equal to rays from the light source located at a limiteddistance. Another method is to advance a part of lenses in the lenssystem in order to correct aggravation of aberrations to be caused whenthe lens system is used for rays from infinite distance. In theobjective according to the present invention, the latter method isadopted. That is, the objective according to the present invention isarranged to vary the airspace between the second and third lenscomponents by integrally advancing the first and second lens componentsin order to favourably correct aberrations for rays from infinitedistance. The range of the most preferable amount of variation Δd₄ ofthe airspace d₄ for attaining the above-mentioned object is defined bythe following condition.

    0.5 > Δd.sub.4 /f > 0.2                              (6)

When the objective for the light source at a limited distance is usedfor rays from infinite distance as it is, overcorrection of sphericalaberration occurs, and this is corrected favourably when said amount ofvariation Δd₄ is within the range defined by the condition (6). If theamount of variation Δd₄ becomes Δd₄ /f < 0.2, spherical aberration willremain still overcorrected. On the other hand, if it becomes Δd₄ /f >0.5, spherical aberration will be undercorrected and, moreover, sinecondition will be overcorrected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view of the objective according to the presentinvention;

FIGS. 2A, 2B, 2C and 2D respectively show graphs illustrating aberrationcurves of the Embodiment 1 of the present invention;

FIGS. 3A, 3B, 3C and 3D respectively show graphs illustrating aberrationcurves of the Embodiment 2 of the present invention;

FIGS. 4A, 4B, 4C and 4D respectively show graphs illustrating aberrationcurves of the Embodiment 3 of the present invention;

FIGS. 5A, 5B, 5C and 5D respectively show graphs illustrating aberrationcurves of the Embodiment 1 when it is used for rays from infinitedistance without correcting aberrations; and

FIGS. 6A, 6B, 6C and 6D respectively show aberration curves of theEmbodiment 1 after aberrations are corrected by integrally advancing thefirst and second lens components.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the objective for video disks according to thepresent invention are as shown below.

    ______________________________________                                        Embodiment 1                                                                  f = 1.0 (where λ = 441.6 nm)                                           r.sub.1 = 2.5497                                                               d.sub.1 = 0.4130 n.sub.1 = 1.46654                                                                         ν.sub.1 = 67.8                               r.sub.2 = -1.4234                                                              d.sub.2 = 0.1335                                                             r.sub.3 = -1.1452                                                              d.sub.3 = 0.1551 n.sub.2 = 1.69827                                                                         ν.sub.2 = 32.1                               r.sub.4 = -123.191                                                             d.sub.4 = 0.0703                                                             r.sub.5 = 2.1641                                                               d.sub.5 = 0.3968 n.sub.3 = 1.46654                                                                         ν.sub.3 = 67.8                               r.sub.6 = -2.7165                                                              d.sub.6 = 1.0766                                                             r.sub.7 = 0.7955                                                               d.sub.7 = 0.2705 n.sub.4 = 1.46654                                                                         ν.sub.4 = 67.8                               r.sub.8 = 6.0546                                                               d.sub.8 = 0.0252                                                             r.sub.9 = 0.3778                                                               d.sub.9 = 0.2777 n.sub.5 =  1.52564                                                                        ν.sub.5 = 64.1                               r.sub.10 = 0.7704                                                              β = -1/40   S.sub.1 = -38.302                                                                         S = 0.224                                        f.sub.F = 3.354  f.sub.R = 0.737                                             Embodiment 2                                                                  f = 1.0 (where λ = 441.6 nm)                                           r.sub.1 = 2.5437                                                               d.sub.1 = 0.4119 n.sub.1 = 1.46654                                                                         ν.sub.1 = 67.8                               r.sub.2 = -1.4293                                                              d.sub.2 = 0.1349                                                             r.sub.3 = -1.1468                                                              d.sub.3 = 0.1439 n.sub.2 = 1.69827                                                                         ν.sub.2 = 32.1                               r.sub.4 = -101.4317                                                            d.sub.4 = 0.0547                                                             r.sub.5 = 2.1904                                                               d.sub.5 = 0.3958 n.sub.3 = 1.46654                                                                         ν.sub.3 = 67.8                               r.sub.6 = -2.7085                                                              d.sub.6 = 1.0741                                                             r.sub.7 = 0.7936                                                               d.sub.7 =  0.2698                                                                              n.sub.4 = 1.46654                                                                         ν.sub.4 = 67.8                               r.sub.8 = 6.0349                                                               d.sub.8 = 0.0270                                                             r.sub.9 = 0.3806                                                               d.sub.9 = 0.2788 n.sub.5 = 1.52564                                                                         ν.sub.5 = 64.1                               r.sub.10 = 0.7966                                                              β = -1/40   S.sub.1 = 38.401                                                                          S = 0.219                                        f.sub.F = 3.366  f.sub.R = 0.735                                             Embodiment 3                                                                  f = 1.0 (where λ = 441.6 nm)                                           r.sub.1 = 2.0768                                                               d.sub.1 = 0.4352 n.sub.1 =1.46654                                                                          ν.sub.1 = 67.8                               r.sub.2 = -1.5056                                                              d.sub.2 = 0.1394                                                             r.sub.3 = -1.1772                                                              d.sub.3 = 0.1399 n.sub.2 = 1.69827                                                                         ν.sub.2 = 32.1                               r.sub.4 = 43.5465                                                              d.sub.4 = 0.0567                                                             r.sub.5 = 1.6841                                                               d.sub.5 = 0.4969 n.sub.3 = 1.46654                                                                         ν.sub.3 = 67.8                               r.sub.6 = -3.6017                                                              d.sub.6 = 0.6995                                                             r.sub.7 = 0.8045                                                               d.sub.7 = 0.3576 n.sub.4 = 1.46654                                                                         ν.sub.4 = 67.8                               r.sub.8 = 2.6438                                                               d.sub.8 = 0.0198                                                             r.sub.9 = 0.3845                                                               d.sub.9 = 0.2663 n.sub.5 = 1.52564                                                                         ν.sub.5 = 64.1                               r.sub.10 = 0.9430                                                              β = -1/40   S.sub.1 = 38.545                                                                          S = 0.2164                                       f.sub.F = 3.036  f.sub.R = 0.786                                             ______________________________________                                    

In the above-mentioned respective embodiments, reference symbols r₁through r₁₀ respectively represent radii of curvature of respectivesurfaces of respective lenses, reference symbols d₁ through d₉respectively represent thicknesses of respective lenses and airspacesbetween respective lenses, reference symbols n₁ through n₅ respectivelyrepresent refractive indices of respective lenses for the wavelength ofλ = 441.6 nm, reference symbols ν₁ through ν₅ respectively representAbbe's numbers of respective lenses for d line, reference symbol frepresents the focal length of the system as a whole, reference symbolf_(F) represents the total focal length of the front lens group,reference symbol f_(R) represents the total focal length of the rearlens group, reference symbol β represents magnification, referencesymbol S₁ represents the distance from the light source to the frontlens surface of the lens system, and reference symbol S represents thedistance from the rear lens surface of the lens system to the recordingsurface.

Aberration curves of respective embodiments shown in the above areillustrated in FIGS. 2A, 2B, 2C and 2D, FIGS. 3A, 3B, 3C and 3D, andFIGS. 4A, 4B, 4C and 4D. When the lens system of the Embodiment 1 isused for rays from infinite distance, aberrations will be correctedfavourably when the airspace d₄ is varied by 0.309f. Aberration curvesof the Embodiment 1 when it is used for rays from infinite distancewithout varying the airspace d₄ are as shown in FIGS. 5A, 5B, 5C and 5D,while aberration curves when the airspace d₄ is varied by 0.309f are asshown in FIGS. 6A, 6B, 6C and 6D. As it is evident from said figures,aggravation of aberrations when the lens system is used for rays frominfinite distance is favourably corrected by varying the airspace d₄.

I claim:
 1. An objective for video disks comprising a front lens groupand rear lens group, said front lens group comprising a first, secondand third lens components, said rear lens group comprising a fourth andfifth lens components, said first lens component being a biconvex lens,said second lens component being a negative lens concave toward saidfirst lens component, said third lens component being a biconvex lens,said fourth lens component being a positive meniscus lens convex towardsaid third lens component, said fifth lens component being a positivemeniscus lens convex toward said fourth lens component, said objectivefor video disks satisfying the following conditions:

    1.19 ≧ d.sub.6 /f ≧ 0.62                     (1)

    3.7 ≧ f.sub.F /f ≧ 2.7                       (2)

    0.29 ≧ f.sub.R /f.sub.F ≧ 0.19               (3)

    0.86 ≧ |r.sub.3 |/|r.sub.2 | ≧ 0.6                                              (4)

    0.15 ≧ d.sub.2 /f ≧ 0.11                     (5)

wherein reference symbol f represents the focal length of the lenssystem as a whole, reference symbol f_(F) represents the total focallength of the front lens group, reference symbol f_(R) represents thetotal focal length of the rear lens group, reference symbols r₂represents the radius of curvature of the rear surface of the first lenscomponent, reference symbol r₃ represents the radius of curvature of thefront surface of the second lens component, reference symbol d₂represents the airspace between the first and second lens components,and reference symbol d₆ represents the airspace between the front andrear lens groups.
 2. An objective for video disks according to claim 1,in which said objective for video disks is further arranged to correctaberrations by varying the airspace d₄ between said second and thirdlens components within the range defined by the condition (6) shownhereunder so that said objective for video disks will be used also forrays from infinite distance:

    0.5 > Δd.sub.4 /f > 0.2                              (6)

wherein reference symbol Δd₄ represents the amount of variation of theairspace d₄ between the second and third lens components.
 3. Anobjective for video disks according to claim 1, in which said objectivefor video disks has the following numerical data:

    ______________________________________                                        f = 1.0 (where λ = 441.6 nm)                                           r.sub.1 = 2.5497                                                               d.sub.1 = 0.4130 n.sub.1 = 1.46654                                                                         ν.sub.1 = 67.8                               r.sub.2 = -1.4234                                                              d.sub.2 = 0.1335                                                             r.sub.3 = -1.1452                                                              d.sub.3 = 0.1551 n.sub.2 = 1.69827                                                                         ν.sub.2 = 32.1                               r.sub.4 = -123.191                                                             d.sub.4 = 0.0703                                                             r.sub.5 = 2.1641                                                               d.sub.5 = 0.3968 n.sub.3 = 1.46654                                                                         ν.sub.3 = 67.8                               r.sub.6 = -2.7165                                                              d.sub.6 = 1.0766                                                             r.sub.7 = 0.7955                                                               d.sub.7 = 0.2705 n.sub.4 = 1.46654                                                                         ν.sub.4 = 67.8                               r.sub.8 = 6.0546                                                               d.sub.8 = 0.0252                                                             r.sub.9 = 0.3778                                                               d.sub.9 = 0.2777 n.sub.5 = 1.52564                                                                         ν.sub. 5 = 64.1                              r.sub.10 = 0.7704                                                              β = -1/40   S.sub.1 = -38.302                                                                         S = 0.224                                       f.sub.F = 3.354   f.sub.R = 0.737                                             ______________________________________                                    

wherein respective embodiments, reference symbols r₁ through r₁₀respectively represent radii of curvature of respective surfaces ofrespective lenses, reference symbols d₁ through d₉ respectivelyrepresent thicknesses of respective lenses and airspaces betweenrespective lenses, reference symbols n₁ through n₅ respectivelyrepresent refractive indices of respective lenses for the wavelength ofλ = 441.6 nm, reference symbols ν₁ through ν₅ respectively representAbbe's numbers of respective lenses for d line, reference symbol frepresents the focal length of the lens system as a whole, referencesymbol f_(F) represents the total focal length of the front lens group,reference symbol f_(R) represents the total focal length of the rearlens group, reference symbol β represents magnification, referencesymbol S₁ represents the distance from the light source to the frontlens surface of the lens system, and reference symbol S represents thedistance from the rear lens surface of the lens system to the recordingsurface.
 4. An objective for video disks according to claim 1, in whichsaid objective for video disks has the following numerical data:

    ______________________________________                                        f = 1.0 (where λ = 441.6 nm)                                           r.sub.1 = 2.5437                                                               d.sub.1 = 0.4119 n.sub.1 = 1.46654                                                                         ν.sub.1 = 67.8                               r.sub.2 = -1.4293                                                              d.sub.2 = 0.1349                                                             r.sub.3 = -1.1468                                                              d.sub.3 = 0.1439 n.sub.2 = 1.69827                                                                         ν.sub.2 = 32.1                               r.sub.4 = -101.4317                                                            d.sub.4 = 0.0547                                                             r.sub.5 = 2.1904                                                               d.sub.5 = 0.3958 n.sub.3 = 1.46654                                                                         ν.sub.3 = 67.8                               r.sub.6 = -2.7085                                                              d.sub.6 = 1.0741                                                             r.sub.7 = 0.7936                                                               d.sub.7 = 0.2698 n.sub.4 = 1.46654                                                                         ν.sub.4 = 67.8                               r.sub.8 = 6.0349                                                               d.sub.8 = 0.0270                                                             r.sub.9 = 0.3806                                                               d.sub.9 = 0.2788 n.sub.5 = 1.52564                                                                         ν.sub. 5 = 64.1                              r.sub.10 = 0.7966                                                              β = -1/40   S.sub.1 = 38.401                                                                          S = 0.219                                        f.sub.F = 3.366  f.sub.R = 0.735                                             ______________________________________                                    

wherein respective embodiments, reference symbols r₁ through r₁₀respectively represent radii of curvature of respective surfaces ofrespective lenses, reference symbols d₁ through d₉ respectivelyrepresent thicknesses of respective lenses and airspaces betweenrespective lenses, reference symbols n₁ through n₅ respectivelyrepresent refractive indices of respective lenses for the wavelength ofλ = 441.6 nm, reference symbols ν₁ through ν₅ respectively representAbbe's numbers of respective lenses for d line, reference symbol frepresents the focal length of the lens system as a whole, referencesymbol f_(F) represents the total focal length of the front lens group,reference symbol f_(R) represents the total focal length of the rearlens group, reference symbol β represents magnification, referencesymbol S₁ represents the distance from the light source to the frontlens surface of the lens system, and reference symbol S represents thedistance from the rear lens surface of the lens system to the recordingsurface.
 5. An objective for video disks according to claim 1, in whichsaid objective for video disks has the following numerical data:

    ______________________________________                                        f = 1.0 (where λ = 441.6 nm)                                           r.sub.1 = 2.0768                                                               d.sub.1 = 0.4352 n.sub.1 = 1.46654                                                                         ν.sub.1 = 67.8                               r.sub.2 = -1.5056                                                              d.sub.2 = 0.1394                                                             r.sub.3 = -1.1772                                                              d.sub.3 = 0.1399 n.sub.2 = 1.69827                                                                         ν.sub.2 = 32.1                               r.sub.4 = 43.5465                                                              d.sub.4 = 0.0567                                                             r.sub.5 = 1.6841                                                               d.sub.5 = 0.4969 n.sub.3 = 1.46654                                                                         ν.sub.3 = 67.8                               r.sub.6 = -3.6017                                                              d.sub.6 = 0.6995                                                             r.sub.7 = 0.8045                                                               d.sub.7 = 0.3576 n.sub.4 = 1.46654                                                                         ν.sub.4 = 67.8                               r.sub.8 = 2.6438                                                               d.sub.8 = 0.0198                                                             r.sub.9 = 0.3845                                                               d.sub.9 = 0.2663 n.sub.5 = 1.52564                                                                         ν.sub.5 = 64.1                               r.sub.10 = 0.9430                                                              β = -1/40   S.sub.1 = 38.545                                                                          S = 0.2164                                       f.sub.F = 3.036  f.sub.R = 0.786                                             ______________________________________                                    

wherein respective embodiments, reference symbols r₁ through r₁₀respectively represent radii of curvature of respective surfaces ofrespective lenses, reference symbols d₁ through d₉ respectivelyrepresent thicknesses of respective lenses and airspaces betweenrespective lenses, reference symbols n₁ through n₅ respectivelyrepresent refractive indices of respective lenses for the wavelength ofλ = 441.6 nm, reference symbols ν₁ through ν₅ respectively representAbbe's numbers of respective lenses for d line, reference symbol frepresents the focal length of the lens system as a whole, referencesymbol f_(F) represents the total focal length of the front lens group,reference symbol f_(R) represents the total focal length of the rearlens group, reference symbol β represents magnification, referencesymbol S₁ represents the distance from the light source to the frontlens surface of the lens system, and reference symbol S represents thedistance from the rear lens surface of the lens system to the recordingsurface.